How to load PDF from the file system

private Stream ReadPdfStreamFromExternalStorage() 
{ 
    // Get the path of the external storage directory. Here, we used the download directory to read the PDF document 
    String path = Android.OS.Environment.GetExternalStoragePublicDirectory(Android.OS.Environment.DirectoryDownloads).AbsolutePath; 
    // Read the specific PDF document from the download directory 
    Java.IO.File filePath = new Java.IO.File(path + "/test.pdf"); 
    // Check whether the file exists in the download directory 
    if (filePath.Exists()) 
    { 
        // Convert the file path to a stream to display it in SfPdfViewer 
        return new FileStream(filePath.AbsolutePath, FileMode.Open, FileAccess.Read); 
    } 
    else 
    { 
        // Throw an exception if the file is not found in the appropriate directory 
        throw new FileNotFoundException("File not found" + filePath.AbsolutePath.ToString()); 
    } 
}  

protected override void OnCreate(Bundle bundle)
{
    base.OnCreate(bundle);
    // Set the activity content from a layout resource
    SetContentView(Resource.Layout.Main);
    // Find a SfPdfViewer that was identified by resource ID
    var pdfViewerControl = FindViewById<SfPdfViewer>(Resource.Id.pdfviewerControl);
    // Read the PDF document as a stream from External Storage
    Stream pdfStream = ReadPdfStreamFromExternalStorage();
    // Load the PDF document stream into SfPdfViewer
    pdfViewerControl.LoadDocument(pdfStream);
}